Phase transformation model for adjusting the cooling conditions in Stelmor process to obtain the targeted structure of thermomechanically rolled wire rod used for fastener production

The paper demonstrates the capability of the developed phase transformation model to design the cooling conditions in the Stelmor process allowing for obtaining different types of microstructures in wire rod of 32CrB4steel. The model based on modified JMAK equation was developed using the results of the tests conducted in a DIL 805 A/D/T dilatometer. The model is composed of sub-models of ferritic, pearlitic, bainitic and martensitic transformations. Its predictive capability was confirmed in industrial conditions by performing trials with different settings of fans involved in the cooling process on the Stelmor line of CMC Poland. Excellent performance of the model was achieved through the modification of commonly used equations which allows accurate predictions of the phase transformations start and finish temperatures, as well as volume fraction of microstructural constituents, in a wide range of cooling rates. It was demonstrated that the model can effectively be applied to design the cooling conditions in the Stelmor process, which will result in the required microstructural composition of the wire rod.